Data reduction for a musical instrument using stored waveforms

Abstract

A keyboard operated musical instrument is disclosed in which the musical tones are generated by reading out data values stored in a waveshape memory. The number of stored data points is reduced by storing the data values in segments corresponding to one-half of the number of data points for a period of a waveshape. By using synthesized data having a symmetry about the midpoint the second half of the waveshape is recovered by a forward and backward memory address read of each waveshape segment. After reading each segment a predetermined number of cycles, an abrupt jump is made to the next segment of waveshape data points.

I claim: 
     
       1. In combination with a keyboard operated musical instrument having an array of keyswitches, apparatus for producing a musical tone comprising; an assignor means whereby a detect data word is generated in response to each actuated keyswitch in said array of keyswitches and one of a plurality of tone generators is assigned to each actuated keyswitch contained in said array of keyswitches and whereby a corresponding detect data word is provided to the corresponding said assigned tone generator, and   said plurality of tone generators each of which comprises, a waveshape memory means for storing a plurality of data words stored in contiguous segments of data words.   a memory addressing means responsive to said provided detect data word whereby a selected segment of data words is read out from said waveshape memory means a preselected number of repetition timing periods before the readout is advanced to an adjacent segment of data words, whereby during each of of said timing periods the stored data words in said selected segment of data words is read out in a first order followed by reading out the same segment of data words in reverse order,   a conversion means for producing a musical tone responsive to data words read out from said selected waveshape memory means.     
     
     
       2. In a musical instrument according to claim 1 wherein said assignor means comprises; a keyswitch state detect means wherein a detect signal is generated in response to each actuated keyswitch in said array of keyswitches, and   an encoding means for encoding each said detect signal to generate said corresponding data detect word which identifies each said actuated keyswitch corresponding to a generated detect signal.   
     
     
       3. In a musical instrument according to claim 2 wherein said assignor means further comprises; a frequency number generating means whereby a frequency number is generated in response to each said detect data word, and   assignor circuitry whereby said generated frequency number is transferred to an assigned one of said plurality of tone generators which corresponds to said detect data word.   
     
     
       4. In a musical instrument according to claim 3 wherein said memory addressing means comprises; a timing clock for providing timing signals,   an adder-accumulator means, comprising an accumulator, responsive to said timing signals for successively adding said generated frequency number to the content of said accumulator to produce an accumulated frequency number, and   a reading means responsive to said generated frequency number and responsive to said accumulated frequency number whereby a selected segment of data words is read out from said waveshape memory means for said preselected number of timing repetition periods.   
     
     
       5. In a musical instrument according to claim 4 wherein said reading means comprises; a first state detect means whereby a first state change signal is generated in response to a binary state change in a preselected bit position of said accumulated frequency number,   a gate means interposed between said timing clock and said adder-accumulator means whereby in response to said first state change signal said timing signals are not transferred to said adder-accumulator means and whereby in response to a second state change signal said timing signals are transferred to said adder-accumulator means,   a number memory means for storing said accumulated frequency number in response to said first state change signal,   a subtract means responsive to said timing signals whereby said generated frequency number is successively subtracted from the accumulated frequency number contained in said number memory means to produce a modified accumulated frequency number,   a second state detect means whereby said second state change signal is generated in response to a binary state change in said preselected bit position of said modified accumulated frequency number,   a data select means whereby in response to said second state change signal said accumulated frequency number contained in said adder-accumulator means is selected and whereby in response to said first state change signal said modified accumulated frequency number in said number means is selected, and   a waveshape reading means for reading out data words from said waveshape memory means in response to the outut from said data select means.   
     
     
       6. In a musical instrument according to claim 1 wherein each of said waveshape memory means stores a plurality of segments of data words and each said segment of data words corresponds to one half of the period of a waveshape having a symmetry about a midpoint having the number of data words as that contained in said segment of data words. 
     
     
       7. In a musical instrument according to claim 6 wherein said conversion means for producing a musical tone comprises; a data conversion means for converting the data words read out from said waveshape memory means to produce said musical tone.   
     
     
       8. In a musical instrument according to claim 5 wherein said waveshape memory means stores a plurality of segments of data words and each said segment of data words corresponds to one half of the period of a waveshape having an odd symmetry about a midpoint having the number of data points as that contained in said segment of data words. 
     
     
       9. In a musical instrument according to claim 8 wherein said conversion means for producing a musical tone comprises; a complementing means whereby a 2's complement binary operation is performed on the data words read out of said waveshape memory means in response to said first state change signal, and   a data conversion means for converting the data words read out from said waveshape memory means to produce said musical tone.   
     
     
       10. In combination with a musical instrument, having an array of keyswitches, in which a musical tone is created by reading out stored waveshape data, apparatus for producing a musical tone comprising; an assignor means for assigning one of a plurality of tone generators to an actuated one of said array of keyswitches, and   said plurality of tone generators each of which comprises, a waveshape memory means for storing a plurality of segments of data words stored in contiguous segments of data words,   a memory addressing means whereby successive segments of data words are read out from said waveshape memory means for a preselected number of repetitions before the read out is advanced to an adjacent segment of data words,   a conversion means for producing a musical tone responsive to data words read out from said waveshape memory means.